import java.util.Arrays;

public class MyStack {
    public  int[] elem;
    public  int usedSize;

    public MyStack(){
        this.elem = new int[10];
    }
    public void push(int val){
        if(isFull()){
            //扩容
            elem = Arrays.copyOf(elem,2*elem.length);
        }
        elem[usedSize] = val;
        usedSize++;
    }
    public boolean isFull(){
        return usedSize == elem.length;
    }
    public int pop(){
        if(empty()){
            return -1;
        }
        int oldval = elem[usedSize-1];
        usedSize--;
        return oldval;


    }
    public int peek(){
        if(empty()){
            return -1;
        }
        int oldval = elem[usedSize-1];

        return oldval;


    }
    public boolean empty(){
        return usedSize == 0;
    }


}
